This application relates to microstructures with a periodic pattern and nanotechnology.
Nanofabrication is a foundation for many different types of nanotechnologies. Periodic nano-island features with the island diameter of larger than ˜50 nm can be relatively easily fabricated using well established photolithography and laser lithography. However, nano island arrays with less than 50 nm feature size, even more preferentially less than 20 nm feature size, are difficult to fabricate with various lithography techniques. Electron beam lithography can be used for such fine features, however, the electron beam lithography can be slow due to the serial processing and many be costly for various large scale industrial applications.
A periodic nano element features such as nano-islands, nano-rods, or nano-cavities are useful as a basis of a variety of nanodevices including electronic, acoustic, photonic, and magnetic devices. Examples of such devices include quantum dot or single electron transistor array, photonic bandgap structures, non-linear acoustic (phononic) devices, ultra-high-density information storage media such as magnetic recording media, phase change recording media, or charge-trapping memory media, and band-gap controlled semiconductor light sources and displays, e.g., incorporating quantum well or quantum dot opto-electronic devices. For efficient addressing and minimizing of defects, interference and noises caused by interactions between adjacent nano-islands, a periodic array with identical location and spacing of nano-islands is highly desirable.
In recent years, there has been much effort to fabricate nanostructures, including nano-islands, nanowires and nanotubes. Several approaches have been actively pursued for creation of such nanostructures, in particular, with an aim of fabricating a periodic nanostructure array. Examples of these approaches include the use of nanoscale, naturally occurring periodic-structured nano templates such as anodized aluminum oxide (AAO) membranes as a host for preparation of new nanostructure arrays, use of colloidal materials that have a surfactant type polymer matrix and inorganic nanoparticles to self-assemble into a periodic array of nanoparticles as the solvent dries up, use of a co-polymer material such as a phase-decomposed and processed diblock copolymer film for nanostructure fabrication. These and other techniques have certain technical limitations. For example, one technical limitation in some implementations of the these techniques is that the region of uniform periodic array is often very small, of the order of e.g., several micrometers or less. For many electronic, optical or magnetic products, the desired area of long-range order of periodic elements (or at least an aggregate of such long-range ordered regions) is on the order of millimeters or centimeters, which the current processing in the prior art can not reproducibly produce.
The non-periodic arrangement of such memory or logic devices or information bits increases the total number of device defects and reduces the effectiveness and usefulness of the nano-patterned device array, as it can cause undesirable electrical shorts, capacitive interactions, noises, interference with too closely located neighboring elements. In the case of magnetic hard disc media, undesirable switching or read errors of magnetically written bits (magnetized along a desired direction) can occur if the neighboring magnetic islands are too closely spaced as compared to other neighbors when the moving read/write head passes by the magnetic bits to retrieve the written information.
Two-dimensional (X-Y) addressable memories or logic devices desirably contain a periodic array of elements which perform a variety of functions. Some examples of x-y addressable functions include; i) electrical functions such as in RRAM (resistive random access memory dependent on change of electrical resistance in the elements by x-y addressing with voltage or current pulses which introduce either amorphous-crystalline phase change or interface electrical resistance change), ii) electric charge-storing functions, e.g., flash memory using storage of trapped electrical charge in floating gate elements, iii) electrical switching functions such as quantum computing quantum dot array, single electron transistor arrays, tunnel junction arrays, iv) optical functions, e.g., magneto-optical memory using laser beam writing/reading in combination with magnetic switching, or phase change material with altered optical properties induced by laser pulse heating, or quantum-dot regime luminescent devices, and v) magneto-electric functions, e.g., MRAM (magnetic random access memory). If the element in the x-y matrix array of devices are non-periodically placed, the device elements are mis-registered with respect to the x-y conductor array lines, and the devices may not be able to function in a desirable manner.
Therefore there is a need for effective processing techniques which provide desirable, long-range orders of periodically placed nano-islands, nano-particles, nano-pores, nano-compositional modifications, or nano-device elements.